The long-term goal of this project is to determine the mechanism(s) involved in the temporal regulation of the expression of DNA repair genes. A thorough analysis of the regulatory mechanisms involved will increase our understanding of cell cycle mediated gene regulation in eukaryotes and our knowledge of the DNA repair strategies cell use to ensure self perpetuation without error. The proposed studies have significant implications for examining the relationship between DNA repair and genetic diseases in which predisposition to cancer is a phenotypic characteristic. The temporal modulation of DNA repair processes appears to be a common feature in mammalian cells of different origins. In addition, there appears to be a correlation between altered cell cycle control of DNA repair processes and DNA repair deficiency or hypersensitivity to damage. However, the exact mechanism of this modulation is unclear. It is clear that Chinese Hamster Ovary (CHO) cells are good models for analyzing the regulation of DNA repair processes and extrapolating to the human model. As part of our continuing effort to understand the regulatory mechanism(s) involved in the temporal modulation of DNA repair processes, we propose to examine the control of DNA repair processes at the molecular level. We will use the recently cloned Chinese hamster apurinic/apyrimidinic (AP) endonuclease gene (CHAPE) as a model. We propose to look at the control mechanisms from several different aspects: 1) To examine whether control of DNA repair processes is at the level of transcription. 2) To construct vectors for the characterization of CHAPE gene promoter; 3) To detect the sequence-specific DNA-binding protein in the crude extracts from the hamster cell lines, AA8 and EM9 and also to identify the specific binding sites for these proteins; 4) To stably transfect CHOAA8 and EM9 cells with the APE_I-CAT promoter constructs; and 5) To check the cell cycle inducibility of the CHAPE gene.